Area Forecast Discussion
Issued by NWS St. Louis, MO

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284
FXUS63 KLSX 181002
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
402 AM CST Sat Nov 18 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 402 AM CST Sat Nov 18 2017

A developing surface low was over east central KS with a
warm front extending northeast to between UIN and PPQ.  Scattered
showers were across parts of northeast and central MO into west
central IL along and north of the warm front.  This surface low will
deepen as it moves east-northeastward along the warm front, and
moves across southern IL into IN later this morning, dragging a
strong cold front southeastward through our forecast area this
morning.  The high resolution models depict embedded elevated
thunderstorms across northeast MO and west central IL this morning
with isolated hail possible.  A few surface based thunderstorms will
develop late this morning into the early afternoon along the cold
front across southeast MO and southwest IL which may produce
isolated damaging winds.  A band of deformation type post frontal
rain and showers will drop southeastward through our forecast area
late this morning and this afternoon associated with the upper level
trough moving eastward through the region.  This precipitation
should shift east of our forecast area by 00Z Sunday.  Will continue
the wind advisory today with very strong and gusty northwesterly
surface winds behind the cold front due to a tight surface pressure
gradient between the deepening surface low moving into the OH Valley
region and the surface ridge over the Plains. Gradient surface winds
at times will be 20 to 30 mph sustained with gusts up to 45 mph. The
strong cold air advection behind the cold front will lead to falling
temperatures after fropa today.  Although temperatures will be
dropping into the 30s across northeast MO and west central IL late
this morning and this afternoon, looking at forecast soundings it
appears that the freezing level will be too high for any change over
to snow.  Could not totally rule out a brief period of snow mixing
in with rain across isolated parts of northeast MO and west central
IL early this afternoon.  It will be cold tonight with continued
cold air advection, a clearing sky, and surface dew point dropping
into the upper teens to lower 20s.  Lows tonight will be 5 to 10
degrees below normal.

GKS

.LONG TERM...  (Sunday through Friday)
Issued at 402 AM CST Sat Nov 18 2017

A longwave upper TROF will persist over eastern North America
throughout this period.  This will "open the door" to several upper
level disturbances to pass thru our region as well as cold fronts
and colder air intrusions to drop in periodically.

As it stands now, most of these upper level disturbances are slated
to pass thru between Monday and Wednesday, but models are also in
good agreement on the atmospheric column being much too dry for a
weak to moderate strength migratory disturbance to have enough time
to saturate much if any of the column.  As a result, dry weather is
expected throughout the forecast period.

Temperatures will see-saw next week, beginning below average on
Sunday in the wake of the strong cold front the day before, but
already will rebound to near 60F on Monday thanks to breezy
southerly winds.  Another cold front will drop thru dry on Tuesday
with another brief bout of below average temps Wednesday and
Thursday.  A return of southerly flow towards next weekend will
begin the next rebound of temps into the 50s and possibly higher
for Friday.

TES

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1141 PM CST Fri Nov 17 2017

Current indications are that most of the are will stay VFR through
most of the night with the exception of parts of northeast
Missouri and west central Illinois. Ceilings will lower to MVFR
and then IFR by 12Z. Isolated showers will increase in coverage
over the area toward daybreak as well, and scattered thunderstorms
will also develop as warm most air continues to move into the
region ahead of a strong cold front. Flight conditions will
deteriorate area-wide during the morning but widespread IFR only
looks likely north of the I-70 corridor. Some patches of IFR CIGS
are possible further south, but should be transient and short-
lived. MVFR CIGS/VSBYS will likely prevail after FROPA in the
afternoon with precipitation ending from west to east by 00Z. Some
of the precipitation may end as a rain/snow mix over northern
portions of the forecast area during the early afternoon. Strong
northwest wind behind the front will likely gust to 35-40kts.
Clouds should rapidly exit the area in the late afternoon/early
evening from west to east and wind is expected to diminish early
Saturday evening. VFR flight conditions are expected thereafter.

SPECIFICS FOR KSTL:

VFR flight conditions are expected to prevail at Lambert for the
rest of the night. Isolated showers will be possible...and there
may be a stray patch of MVFR that moves over the terminal before
12Z. Expect increasing coverage in showers and a few thunderstorms
Saturday morning ahead of a strong cold front. FROPA is expected
between 15Z and 16Z which should bring the chance for
thunderstorms to an end. MVFR ceilings are likely behind the
front...possibly lower...with continuing light rain through the
early to mid afternoon. Expect rain to end before 00Z with clouds
scattering out during the early evening. Strong northwest wind
behind the front will likely gust to between 35-40kts. The wind
should diminish during the early evening.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory until 6 PM CST this evening for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Wind Advisory until 6 PM CST this evening for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX



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